The present invention relates to an image printing apparatus using a printhead and, more particularly, to an image printing apparatus capable of supplying a stable power to the printhead and printing a high-quality image.
Printers which print desired information such as characters or images on a sheet-like printing medium such as a paper sheet or film are adopted as an information output apparatus for a word processor, personal computer, facsimile machine, or the like.
The printing method of the printer includes various methods. An ink-jet method has recently received a great deal of attention because it can perform non-contact printing on a printing medium such as a paper sheet, can easily print a full-color image, and is quiet. As an ink-jet arrangement, a serial printing method is generally widely used in terms of low cost and easy downsizing. In the serial printing method, a printhead for discharging ink in accordance with desired printing information is mounted. Information is printed by reciprocally scanning the printhead in a direction perpendicular to the feed direction of a printing medium such as a paper sheet.
FIG. 6 is a block diagram showing a supply system which supplies power and an image signal from a conventional ink-jet printer main body to the printhead. FIG. 7 is a side view showing a carriage electric mounting portion mounted on the carriage of the conventional printer.
In the conventional ink-jet printer, a power supply for supplying power is incorporated as a power supply unit board 103 in the printer main body, as shown in FIG. 6, or is connected as an AC adapter (not shown) to the printer main body. Necessary power is supplied to a printhead 102 connected to a carriage board A 100 mounted on the carriage via a power supply wiring pattern 105 on a main body board 104 and via a flexible wiring conductor (flexible wiring board or wiring line called xe2x80x9cflat cablexe2x80x9d) 101.
Recent printers are required to achieve high quality equivalent to a photograph (to be referred to as photographic quality hereinafter) and performance of printing an image at a high speed (to be referred to as high-speed printing hereinafter). The ink-jet printer technique has remarkably been developed, and the above-described conventional power supply method poses the following problems.
More specifically, to meet both the photographic quality and high-speed printing, it is necessary that xe2x80x9csmall ink droplets are discharged from the printing elements of the printhead 102 to a printing medium (e.g., printing sheet) as much as possible per unit timexe2x80x9d. The ink-jet printer must satisfy this demand. For this purpose, the electric energy (power) per unit time necessary for printing to be supplied to the printhead 102 must be increased.
The power supply for supplying power is generally a constant-voltage power supply. To meet both the photographic quality and high-speed printing, a current (IPrhd) supplied to the printhead 102 as a load is increased by the load.
The above-mentioned flexible wiring conductor 101 generates the following voltage drop (VDrop) owing to its wiring resistance (RFrex):
VDrop=IPrhdxc3x97RFrex
The voltage drop VDrop) changes depending on an image to be printed by the printhead 102. With an excessively large voltage drop VDrop), a voltage supplied from the power supply for supplying power becomes lower than a voltage necessary for the printhead 102 to print an image. As a result, ink necessary to print an image may not be able to be supplied from the printing element.
To solve this problem, the voltage drop (VDrop) by the wiring resistance (RFrex) is suppressed to be small. In order to reduce the wiring resistance (RFrex) of the flexible wiring conductor 101, the power supply line has been made thick or the number of power supply lines has been increased.
In these measures, the flexible wiring conductor 101 functions as a physical load to the carriage, and causes various problems: (1) the load of the carriage driving motor increases; (2) the rigidity of the power supply line increases to impair the flexibility of the wiring conductor 101; and (3) the cost of the wiring conductor 101 increases.
Especially in a large A0-size ink-jet printer, the flexible wiring conductor 101 is longer than that of an A4-size home printer, and exceeds 1 m including internal wiring. Thus, the above-described problems become serious, and electric energy (power) necessary for printing to be supplied to the printhead 102 cannot be satisfactorily supplied.
As one solution for the problem, an example of mounting a power supply for supplying power on the carriage is disclosed in Japanese Patent Laid-Open No. 10-6505 (Hewlett-Packard) xe2x80x9cCarriage-Mounted Printed Circuit Assembly to Which Pen Driver and Power Supply Circuit Are Assembledxe2x80x9d.
When, however, the arrangement disclosed in Japanese Patent Laid-Open No. 10-6505 was applied to an actual ink-jet printer, the following problems 1 and 2 occurred, and it was found that the ink-jet printer could not be easily constituted.
[Problem 1]
No mounting space can be ensured on a carriage board A 110 due to restrictions on the printing direction.
FIG. 8 is a block diagram showing the power supply system of an ink-jet printer when a power supply (DC/DC converter) for supplying power is mounted on the carriage board A 110. FIG. 9 is a side view showing a carriage electric mounting portion when the power supply for supplying power is mounted on the carriage board A 110.
In printing an image, as shown in FIG. 7, a conventional ink-jet printer discharges ink droplets from the lower surface of the printhead 102, and a printing sheet as a printing medium is fed below the lower surface.
To mount the power supply for supplying power on the carriage board A 110, as shown in FIG. 9, the carriage board in FIG. 7 must be enlarged upward, and the power supply must be mounted on the enlarged carriage board. However, if the board is enlarged upward, as shown in FIG. 9, the board hits against the cover of the ink-jet printer main body. The conventional outer cover cannot be directly used, and the specifications must be changed to enlarge the outer cover.
This specification change increases not only the manufacturing cost but also the ink-jet printer installation volume. This degrades the compactness in installation which is one of important product properties of the ink-jet printer. Also when the carriage board A 110 is enlarged (not shown) in the carriage moving direction (main scanning direction, i.e., right-to-left direction viewed from the front of the printer) in order to mount the power supply for supplying power, the outer case must be enlarged in the right-to-left direction, increasing the installation area. Also in this case, the same problems as those described above occur.
[Problem 2]
Large-format printers are mainly for business purposes. Due to heavy duty, a load change absorbing decoupling capacitor (also serving as an output capacitor for a DC/DC converter) must be exchanged, which is difficult to perform.
In FIG. 6, the current IPrhd) supplied from the power supply unit board 103 to the printhead 102 changes in accordance with the printing image, as described above. The printing elements (nozzles) of the printhead 102 change from xe2x80x9ca state in which no ink is dischargedxe2x80x9d to xe2x80x9ca state in which all nozzles assigned for simultaneous driving discharge inkxe2x80x9d. The load change changes the driving voltage of another head board (HB) mounted in the printhead. To prevent the voltage change, a load change absorbing decoupling capacitor 106 is mounted.
To satisfy both the photographic quality and high-speed printing, the electric energy amount (power) supplied to the printhead increases in proportion to the load. Along with this, the load changes greatly, and a large ripple current (Icripple) flows into the load change absorbing decoupling capacitor 106. The decoupling capacitor 106 generates heat by itself owing to the equivalent series-resistance (ESR) of the decoupling capacitor 106 and the flowing ripple current (Icripple), shortening the service life of the decoupling capacitor 106.
Particularly in a heavy-duty, large-format business ink-jet printer, a printhead 112 is set as a replaceable component with a fatigue life. The arrangement of the load change absorbing decoupling capacitor 106 is set in advance so as to allow replacing it in periodic maintenance. This is convenient for the user because he/she can use the ink-jet printer main body for a long term. In the conventional ink-jet printer, however, the arrangement is not set in the above way, and it is difficult to replace a degraded load change absorbing decoupling capacitor.
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide an image printing apparatus capable of stably supplying to a printhead a voltage necessary to realize stable image printing, and maintaining a compact shape in an ink-jet printer required for a larger area, higher photographic quality, and higher-speed printing in the future.
To achieve the above object, an image printing apparatus according to an aspect of the present invention has the following arrangement. That is, there is provided an image printing apparatus in which a carriage which supports a printhead having a plurality of printing elements is scanned on a printing medium on the basis of input printing data to print an image, the carriage comprising a first print circuit board having voltage conversion means for converting a voltage supplied from an apparatus main body, and a second board having smoothing means for smoothing the converted voltage, and the printhead using the smoothed voltage as driving power.
For example, the voltage conversion means preferably comprises a voltage conversion circuit which increases or decreases the supplied voltage.
For example, the smoothing means preferably includes a capacitor.
For example, the first print circuit board and the second print circuit board are preferably connected by a power supply line which supplies driving power to the printhead.
For example, the power supply line preferably comprises a power supply line for supplying power and a plurality of GND lines having different GND potentials.
For example, one of the plurality of GND lines is preferably connected to a constant-voltage control circuit of the voltage conversion means.
For example, it is preferable that the image printing apparatus comprises a main body print circuit board having generation means for generating an image signal to be transmitted to the printhead, and the first print circuit board and the main body print circuit board be connected by a flexible electric wiring line.
For example, the first print circuit board and the main body print circuit board preferably further comprise signal transmission buffer means for stably transmitting and receiving the image signal.
For example, the signal transmission buffer means preferably stably transmits and receives the image signal by using an LVDS (Low Voltage Differential Signaling).
For example, the image printing apparatus preferably comprises an ink-jet printhead which discharges ink to print information.
For example, the printhead preferably includes a printhead which discharges ink by using heat energy, and comprises a heat energy converter for generating heat energy to be applied to ink.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.